1. Field of the Invention
This invention relates to apparatus for cleaning and magnetizing pipes prior to inspection of the pipes for anomalies which may later cause structural failure.
2. Discussion of Related Art
Oil country tubular goods commonly known as OCTG pipe must be thoroughly inspected prior to being placed in service. The most common and economical method of inspection is a technique known as magnetic flux leakage inspection. In this method, the pipe is magnetized and the flux diversion about a defect is found by means of electronic scan systems or magnetic powder applications. One of the methods of magnetization is to pass the current (in excess of 3000 amperes DC) through a conductor placed axially within the pipe. The current induces a circumferential magnetic field in the pipe. Imperfections in the pipe are outlined by the flux leakage to the inside or outside surface of the pipe.
In addition to the magnetization process, it is necessary to thoroughly clean the inside and outside surfaces of the pipe. This is done by passing the pipe through a machine which applies powered brushes to the outside and (by means of a brush mounted on a lance) inside surfaces of the pipe. The belief has long been held that cleaning pipe by any method subsequent to magnetization thereof would destroy the magnetic field and the ability to perform the inspection function. Accordingly, the cleaning and magnetization of pipe has always been carried out as separate operations.
U.S. Pat. No. Re. 26,537, reissued Mar. 4, 1969, to Tompkins, shows an apparatus for the inspection of longitudinal pipe members. The Tompkins device is preferably mounted in a van-type vehicle and includes electric motors for translating a tubular member longitudinally along a rack. The pipe is translated through the van by passing through the rear of the truck where a stationary inspection head inspects the pipe for circumferentially extending flaws. The pipe is then translated onto a rack to engage an axially centered conductor which is positioned in the pipe by motion of the pipe. The conductor conducts a surge of current to form a residual magnetic field in the wall of the pipe. U.S. Pat. No. 3,535,623, issued Oct. 20, 1970, to Wood et al, and U.S. Pat. No. 3,535,624, issued Oct. 20, 1970, to Wood, show devices for the inspection of tubular members wherein a rigid lance is mounted at an end and spaced from its free end are suitable centralizers, a circumferential set of inside surface detection shoes for detecting a longitudinal field and one or more inside surface detection shoes for detecting a circumferential field.
U.S. Pat. No. 3,539,915, issued Nov. 10, 1970, to Walters et al, shows a device for magnetizing sections of tubular goods wherein a circumferential flux is produced by high current pulses applied to successive overlapping longitudinal sections of a pipeline using axially spaced conductive brushes or spurs. A similar apparatus is shown in U.S. Pat. No. 3,593,122, issued July 13, 1971, to Barton et al. The Barton device includes an apparatus wherein hard spots are detected in a steel pipeline by measuring both active and residual magnetic flux fields. The magnetic flux field is produced by pole pieces which may be circular disks or radially extending spoked or webbed members which support at their peripheries respective wire brush members and which have flexible flux conducting bristles that make contact with the full circumference of the inner wall of the pipeline and conduct magnetic flux thereto.